A proline acylase (N-acyl-L-proline amido hydrolase) from a pseudomonas strain is described in Biochimica et Biophysica Acta, 744 1983), pp. 180-188, Elsevier Biomedical Press. That enzyme is very rapidly inactivated at a temperature as low as 50.degree. C. However, enzymes are required for industrial use which have a high degree of stability. It is especially advantageous to carry out the reaction at elevated temperatures, which considerably raise the reaction speed and the solubility of the substrates, but this requires an enzyme which can withstand such temperatures.